1. Field of the Invention
The present invention relates to the art of making tie-ins or connections between pipelines for use in subsea environments. Where the site of the pipelines and their connection is in relatively shallow water, the method and means of connection may be relatively uncomplicated. However, in deep water of several hundred meters or more, increasing problems are encountered in making such connections. While the present invention may be advantageously used even in shallow waters, e.g. fifty meters or less, it is especially valuable in that it may be successfully employed in connecting lines for use at depths of five hundred meters and more.
2. Description of the Prior Art
There are presently two main techniques for making tie-ins in deep water subsea pipelines, and both are expensive and fraught with difficulties. In the first, the ends of the two lines to be connected are engaged by lifting apparatus carried by suitable vessels and are raised out of the water while the connection is made. The vessels used for this service must be relatively specialized and are therefore extremely expensive. Since the pipeline ends being connected must be stabilized, it is necessary to wait for relatively calm seas before attempting to make the connection, and such delays entail further expense. Even under ideal conditions, the movements of the supporting vessels in the water are extremely troublesome, particularly where the connection is made by welding. Expensive, heavy duty equipment is employed to fix the pipeline ends, and in the process, the pipelines may be subjected to deleterious stresses and strains.
The second common technique of making pipeline tie-ins involves making the connection at the bottom of the body of water. Again the process is expensive due to the need for expensive deep water diving bells, highly trained divers, etc. Furthermore, the process is dangerous in that fire and other malfunctions are more imminent under the high pressures existing at such depths. The divers can work for only a relatively short time at the great depths involved and, after each work period, must undergo decompression periods greatly exceeding the amount of time actually spent working. Even with proper work periods and decompression, such work is extremely grueling and frequently injurious to the drivers' health.
It can thus be seen that there is great need in the field for a simpler, safer, and less expensive technique for making tie-ins in subsea pipelines, especially in view of the current emphasis on increasing supplies of readily available fossil fuels.